This invention relates to vane compressors for use as refrigerant compressors in automotive air conditioning systems or like systems, and more particularly to variable capacity vane compressors of the type that the compressor capacity is controlled by varying the timing of commencement of compression.
Variable capacity vane compressors of this type have been proposed e.g. by Japanese Provisional Patent Publication (Kokai) Nos. 62-20688 and 62-129593. These proposed vane compressors are constructed as shown in FIG. 1 through FIG. 4. As shown in FIGS. 1 and 2, a rotor B is rotatably fitted within a cylinder formed by a cam ring A and two side blocks closing opposite ends of the cam ring A, and carries vanes D.sub.1 -D.sub.5 radially slidably fitted in respective slits formed in the outer peripheral surface thereof. Two compression spaces C.sub.1 and C.sub.2 are defined within the cylinder by the inner peripheral surface of the cam ring A and the outer peripheral surface of the rotor B at diametrically opposite locations. During the suction stroke when compression chambers each defined between adjacent two vanes increase in volume, compression fluid is drawn from a suction chamber into the compression chambers through refrigerant inlet ports E and E, as shown in FIG. 3. During the compression stroke following the suction stroke, when the compression chambers decrease in volume, the drawn compression fluid is compressed to be discharged through refrigerant outlet ports F and F and discharge valves G and G into a discharge pressure chamber. An annular recess I is formed in an end face of one H of the side blocks formed with the refrigerant inlet ports E and E, which end face faces the rotor B. Two pressure working chambers J and J are defined in the annular recess I at diametrically opposite locations, which communicate with the suction chamber and the discharge pressure chamber. A control element L is rotatably fitted in the annular recess I, which has a side surface thereof formed with two pressure-receiving protuberances K and K slidably fitted in the respective pressure working chambers J and J to divide each of them into a first pressure chamber communicating with the suction chamber and a second pressure chamber communicating with the discharge pressure chamber, such that the control element is rotatable in opposite directions in dependence on the difference in pressure between the first and second pressure chambers, between a maximum capacity position and a minimum capacity position. The control element L has an outer peripheral edge thereof formed with two arcuate cut-out portions L.sub.1 and L.sub.2 at diametrically opposite locations, which determine the timing of commencement of compression stroke such that the fluid compression starts when a trailing one of two adjacent vanes passes a leading end of each cut-out portion L.sub.1, L.sub.2 in the direction of rotation of the rotor B. The timing of commencement of compression can thus be varied through the whole range as the control element L is rotated between the maximum capacity position as indicated by the solid lines in FIGS. 1 and 3 and the minimum capacity position as indicated by the two-dot chain lines in FIGS. 2 and 3 so that the compression amount or capacity varies between the maximum value as shaded in FIG. 1 to the minimum value as shaded in FIG. 2.
However, according to the above proposed vane compressors, if the location of the leading end of each cut-out portion L.sub.1, L.sub.2 is shifted so as to further retard the timing of commencement of compression when the compressors are in the minimum capacity position and hence further decrease the minimum compression amount in order to increase the variable range of the compressor capacity, this causes insufficient compression, because there is a fixed "dead volume", that is, a non-compressed volume, in each refrigerant outlet port F, F, and therefore if the minimum compression amount is decreased, the ratio of the dead volume to the minimum compression amount increases, causing insufficient compression. Furthermore, since the two cut-out portions of the control element L are located at diametrically opposite locations and accordingly the two compression spaces C.sub.1 and C.sub.2 have the same timing of commencemnt of compression, the above-mentioned insufficient compression will take place in both of the two compression spaces C.sub.1 and C.sub.2 if the minimum compression amount is decreased as above. As a result, the compressors cannot provide desired discharge pressure when they are in the minimum capacity position.